Try understand the files
Compobj
Here you asign how you competiton will be, the numbers of the left line will control the rest of files
Here you regulate the structures of the tournaments and competitions from FIFA. Inserting a complete new tournament is not possible, but replacing an existing one is definitely possible.
Please note that if you add an additional round to a cup, you must also change all other competitions, `cause all stages, rounds and more are numbered here. It’s important for do not lose their connection to each other ... is a very complicated story.
The numbers here will control rest of files if Copa del Rey is in line 1875 you can check the schedule and other configuration in line 1875,1876,1877 etc.
Initeams
Here you assign the competitions, including all their stations, to the teams. Try to do it like EA if you can't go to next season check this file
Schedule
If you replace an existing league and, for example, assign it to a league association (promotion and relegation), it is of course important to create an existing game plan or calendar.
Once you've gotten into it, that's actually one of the easiest changes.
Settings
All competitions and tournaments are managed here. Promotion and relegation, prize money, relegation markings, table sorting, start dates and and and.
Tasks
Important for FIFA to know what to do with the leagues and teams before and after a season.
Weather
Self-explanatory ... here you should choose an existing weather system for the appropriate region of the league.
Advancements
How the teams will advance in the stages you assign
Standings
How many teams there will be in every stage